The present invention relates to a traffic shaping method and system for a virtual path or a virtual connection in a packet switch of a cross connector or a switch for a fixed-length packet, and more particularly to a re-arrangement control method and system for a burst packet arriving from a subscriber line. Specifically, it is suitable for a cell switch in an apparatus using an ATM (Asynchronous Transfer Mode) system.
In the ATM system which complies with the international standard of the CCITT (International Telegraph and Telephone Concultative Committee) in regard to a broadband and multimedia communication in a communication field, a fixed-length packet named a cell is used to effect transmission and switching. Many switch systems for switching the cells have been proposed.
Further, in a transmission apparatus for connecting between switching systems, a virtual line named a virtual path is used as a unit to modify the architecture of the network flexibly and simplify the administration of the line. In this case, it is able to establish a plurality of virtual channels in each virtual path to realize plural pairs of inter-terminal communications on the same path by providing each cell with a virtual path identifier and a virtual channel identifier to discriminate its connection. An apparatus for switching the cell in accordance with the virtual path is employed and this apparatus is named an ATM cross connector. This cross connector is considered to be a kind of ATM switch.
One of the ATM switch system is a shared buffer memory switch. An example of its arrangement method is described in an article "LSI IMPLEMENTATION FOR SHARED BUFFER TYPE ATM SWITCH" by Kosaki et al., Technical Report of the Institute of Electronics, Information and Communication Engineers of Japan, SSE89-144, pp. 49-54 (February, 1990) and is shown in FIG. 2.
Generally, various terminal equipments connected to a subscriber line produce a so-called burst traffic having a period in which data is continuously produced and a period in which no data is produced. When an ATM switching system accommodates such a burst traffic, an amount of buffers required in the ATM switching system is known to require ten and several times to several tens times as large as that in the case where the traffic in which the cell occur at random is accommodated. Accordingly, in order to arrange the ATM network economically by using the cross connector having less amount of buffers, it is necessary to eliminate the burst traffic in the apparatus which accommodates the subscriber lines. To this end, it is necessary to arrange the cells belonging to the same virtual channel or virtual path extremely uniformly in time. This procedure is named the traffic shaping.
A method of effecting such a traffic shaping is described by way of example in an article "PATH HANDLING IN ATM NETWORKS" by Shigesada et al., Technical Report of the Institute of Electronics, Information and Communication Engineers of Japan SSE89-120 pp. 31-36 (January, 1990). More particularly, a system is described in which the traffic shaping is effected by previously determining a time position of the cell belonging to the virtual path or the virtual channel within a frame in an output of the switching system or the cross connector. Further, an algorithm for defining the time position for each output dynamically is also described.
In the switch arrangement by a shared buffer memory switch using the above conventional technique, the traffic shaping is not considered. Accordingly, the line having the burst traffic is switched and delivered while preserving the burst characteristic. As a result, there is a problem that a large amount of buffer memories are required in the cross connector or the switch connected to the output.
Further, even if the traffic shaping for each output is made by the above conventional technique, it is necessary to change the order of time in order to effect the traffic shaping. In this case, since a waiting buffer is required, there is a problem that a great number of buffers are required for a traffic shaping apparatus. On the other hand, by using the algorithm shown in the above conventional technique for dynamically defining the time position, reduction of the memory capacity is also shown. However, since an apparatus for executing this algorithm is complicated and it is necessary to lengthen the period of determining the arrangement to effect more uniform arrangement, there is a problem that the memory capacity is increased.
Further, when the memory capacity is increased, there is a problem that the time that the cell stays in the memory is made long and the delay in the transmission and switching is increased.